There are many systems and methods for testing the strength of an adhesive bond between two materials of a structure. Some systems and methods are designed to detect the strength of an adhesive bond in a non-destructive manner while the bond is in situ or intact. For example, laser bond inspection techniques can be used to detect the strength of an adhesive bond by transmitting a laser-induced stress wave through the bonded structure. The stress waves are initiated at a top surface as compression waves that convert into tension waves upon reflecting off of a second free surface of the structure (which can be a bottom surface). The tension waves apply opposing tension forces onto the two materials forming the bond to effectively pull apart the materials along the bond.
Various conventional surface motion detectors may be used to detect the motion of the surfaces during a laser bond inspection process. For example, electromagnetic acoustic transducers (EMAT) and a velocity interferometer system for any reflector (VISAR) are available for detecting the motion of the surfaces of bonded materials. EMAT transducers use a magnet and a coil to detect motion of a conductive foil adhered to the surface of the bonded material. In one application, the EMAT sensor detects an electric current in the conductive foil due to the stress wave induced motion of the foil in the magnetic field.
Depending on the strength of the bond, the application of a laser-induced stress wave into bonded materials may create defects in the structure. These defects will occur at the weakest part of the structure often in the form of a separation or disbond at the bondline or delamination in the composite structure itself. Disbonds are a separation of the previously bonded surfaces, which can be detected using conventional ultrasound. Accordingly, the detection of such disbonds after a laser bond inspection process may be desirable. Some ultrasonic inspection techniques are available to detect the presence of disbonds within a bonded material. Ultrasonic inspection techniques include using ultrasonic transducers to impart a vibration into a material and measure the resultant feedback vibration. Depending on the characteristics of the feedback vibration, a user can identify locations in the material where the bond has abnormalities or defects. Some ultrasonic techniques are performed using a hand probe. However, such ultrasonic techniques do not provide precise results or results with a high level of detail. For more precise results, many ultrasonic inspection techniques employ an immersion tank and scanning bridge, with the bonded materials being tested submersed in the immersion tank.